This invention relates generally to liquid propellant guns and more particularly to liquid monopropellant guns in which the breech is lined with propellant that is sequentially ignited in a discrete series of small volumes.
The design of a practicable gun weapon system based on the utilization of liquid propellants has been for at least twenty-five years a recurring, but elusive, goal of modern ordnance technologists. The following is quoted from a recent book ["Ignition! An Informal History of Liquid Rocket Propellants," Rutgers University Press, 1972], by Dr. John D. Clark, a noted authority and pioneer in the development of liquid propellants:
"Even a low-energy monopropellant has more energy in it per gram than does smokeless ball powder, and a great deal more energy per cubic centimeter. (A liquid is much more closely packed than a heap of small grains.) So, if a liquid propellant were used, either packaged in the cartridge as the solid propellant is, or pumped separately into the gun chamber behind the bullet, it should be possible to get a much higher muzzle velocity without any increase in weight. Hydrazine-hydrazine nitrate-water mixtures have been the usual propellants in the liquid gun programs, although NPN sometimes mixed with ethyl nitrate, has been running, on and off, since about 1950, but have never been carried through. The military demands a weapon, programs are started and run for a few years, then money or interest runs out, and the whole thing ends, only to start all over five or six years later. I've seen three cycles since I got into the business. JPL, Olin Mathieson, Detroit Controls, as well as various Army and Air Force installations, have been involved. The main problems are more in the engineering than in the chemistry."
The one unequivocal disadvantage which continues to prevent the exploitation of liquid monopropellants in guns is that they are characterized by an unstable, unpredictable, and heretofore uncontrollable combustion process. In bulk loaded liquid monopropellant guns this factor has inevitably produced high and erratic combustion pressures which damage the guns, cause erratic behavior of gas operated weapons, and result in large muzzle velocity variations. It has been shown theoretically and confirmed experimentally that gross hydrodynamic instabilities characterize the normal behavior of bulk loaded liquid propellants in a gun environment. Extensive theoretical treatments of known types of hydrodynamic instabilities believed to be present, viz. the Taylor and Helmholtz instabilities, has served to confirm the fact that the combustion process of bulk loaded liquid monopropellants in a gun cannot be easily controlled.
Current technical approaches to the development of new liquid propellant gun weapon systems, particularly those intended for naval surface warfare, are directed toward the use of bulk load liquid monopropellants for reasons of safety and logistics. The central technical problem to be solved continues to be the requirement for a feasible means of controlling the combustion process to achieve reliable gun interior ballastics. In the search for a solution to this problem the present invention provides an approach which embodies a mechanically controlled combustion process rather than one which relies on natural hydrodynamic processes. It is believed that such an approach can provide a practicable liquid monopropellant gun which avoids altogether the enormously complex and analytically intractable hydrodynamic phenomena associated with previous bulk loaded liquid propellant guns.